Hydraulic double-action draw press



Aug# 29 1944- A. K. NowAK ETAL 2,357,019

HYDRAULIC DOUBLE-ACTION DRAW PRESS Filed-Oct. 5. 1942 4 Sheets-Sheet lTm" mi "Wm I Aug. 29, 1944. A. K. NOWAK Erm. 2,357,019

HYDRAULIC DOUBLE-ACTION DRAW PRESS Filed Oct. 5, 1942 4 Sheets-Sheet 2WQK HOL PRESSURE SWITCH Ream rias RELWM "l NQ wu vf wn ve Sl /E PRESSURE5 Wl 7CH Aug. 29, 1944. K, NOWAK ETAL 2,357,019

HYDRAULIC DOUBLE-ACTION DRAW PRESS Filed Oct. 5, 1942 4 Sheets-Sheet 3Ff J 3a Qn 3 7a 7 50 F- romN 66 m K f 50 54 A, X

,7J s d# 7;0 J riva/vx U L TTNK I P/LDT PRESSURE I7 PLOTPPESSURE Aug.29, 1944. A K. NowAK Erm. 2,357,019

HYDRAULIC DOUBLE-ACTION DRAW PRESS Filed Oct. 5, 1942 4 Sheets-Sheet 4/mr PRESSURE s-wmflhaf E 61 PRESSURE I Sar/uy UNITED STATE,

Patented Aug. 29, 1944 s PATENT OFFICE Ill., assignors to ClearingMachine Corporation, Chicago, Ill., a corporation of IllinoisApplication October 5, 1942, Serial No. 460,840

valves, which latter in turn control the opera- 9 Claims.

This invention relates; in general, to presses, but more speciiically tohydraulic presses which embody hydraulically operated means Aforactuating both a blank or Work-holding slide and a work-performingslide. y

Heretofore, in presses of this general character, the motion of thework-performing slide has been employed as a means for generating uidpressure which has been utilized to actuate an auxiliary hydraulic ramfor increasing or intensifying the pressure of the work-holder upon thework. That is, when one slide is forced down to operate upon the work,the same downward force will cause pressure in the cylinders of theblank or work-holding slide, so that a greater pressure `upon thework-performing slide will be acquired.

It has also been customary, in presses of this y character, to provideseparate sources of fluid pressure; that is, one source for theoperation of the slides, and an independent source of fluid pressure foroperating the other orblank-hold'- ing slide, the clamping orblank-holding slide being independently operable.

It is one of the objects of the present invention to provide an improvedhydraulically operated double-action press, in which the blank orwork-holding slide is not independently operable, but the operation ofwhich is a part of the cycle of operation of the press.

A further object is to provide a press of this character, in which therelative movementl of the slides is utilized, not as Ia means forgenerating, or increasing pressure, but for the purpose of maintainingthe predetermined generated pressure `which acts upon the blank or workholder.

A further object, is to provide in a press of this character, improvedmeans for pre-iilling the cylinders to lill the voids or spaces createdby the relative movement of the cylinder and piston Ielements withoutincreasing the pressure in the system.

A further object is to provide an improved press of this character, inwhich one of the slides is supported by the other slide to movetherewith and with respect thereto, and improved means whereby the workshaping or performing slide will be maintained against engagement withthe work in advance of the blank or work-holding slide, the latter beingdirectly lifted by the inner slide, and being controlled in its movementtoward and away from the work by the movement of the inner slide.

A further object is to provide, in -a pressl of this character, animproved pilot iiuid pressure tures of novelty in substantially theconstruc-V tion of the iiuid pressure upon the respective parts.

To the ,attainment of thse ends and the accomplishment of other new anduseful objects as will appear, the invention consists in the feation,combinatian and arrangement of the several parts, hereinafter more fullydescribed and claimed' and shown in the accompanying drawingsillustrating this invention, and in which- Fig. 1 is a perspective viewof a pressof this character, constructed in accordance with theprinciples of this invention.

Fig, 2 is 'a view, in diagram, of a portion of the press frame and theslides oi the hydraulic system employed in the operation of the press,portions of the press and slides, with the actuating mechanisms, beingin elevation, and portions in section.

' Fig. 3 is a view, in diagram, of a portion of the system, andillustrating,l partly in elevation and partly in section, some of thevalve mechanisms. I l

Fig. V4 is a view of the three-way valveV shown in Fig. 3, and showingsuch valveln a different position.

Figs. 5, 6 and 'I' are sectional views of the main control valve forcontrolling the direction of ow of the iluid, and showing the valve indifferent positions.

Referring vmore particularly to the drawings, in Fig. 1 there is shown apress having a base I0,

' uprights II, and a crown I2, and supported by Connected with the innerslide is is a. piston' member 2|, which extends into and operates system-for controlling the operation of the.

within a cylinder 22, the latter being supported by the press frame. Asa means for permitting and also regulating relative movement of theslides, one with relation to the other, there may be provided a rod orbolt 23 which passes through a portion 'of the inner slide I5 and isprovided with a head 24. The other end o1' the rod passes through aportion 25 of the outer slide, and is screw-threaded to receive nuts orcollars 26 dis- In order to prevent the rod or bolt 23 from rototingwith respect to the parts with which it is connected, there may beprovided a slot or keyway 21 -for the reception of a screw or bolt 28.

With this construction, it will be manifest that the slides may berelatively moved in one direction, as the rod 23 passes freely throughthe portion I of the inner slide, and the relative movement in theopposite direction will be limited by the engagement of the head 24 withthe portion I5 of the inner slide. Obviously, the degree or extent ofsuch relative movements may be varied vat.will, by adjusting the nuts orcollars 26 upon the rod or bolt 23.

The pistons and cylinders lil-,20 constitute pressure-creating units forapplying pressure against the outer slide I4 when the latter is inengagement with the work. The cylinder and piston elements 222|constitute a unit whereby the inner slide I5 may be lowered and raised,and also serve to create pressure upon the inner slide I5 when work isbeing performed.

The outer slide I4 is supported by means of the inner slide I5 andpiston 2| operating in the cylinders 22, by fluid pressure operatingupon the portion 30 of the piston 2|, in a manner to be described.

Connected with the outer` slide I4 are cylinders 3| in which pistons 32operate, and these pistons 32 are connected to the inner slide I5, 'sothat when 'there is a relative movement between these slides, thepistons 32 will be moved with respect to their respective cylinders 3|.Any number of the cylinder and piston elements above described may beemployed.

Leading from each of the cylinders 3| is a pipe or passage 33, each ofwhich communicates,

respectively, with a passage 34 in the respective pistons I8, so thatwhen fluid is in the cylinder 3| and the slides I4 and I5 are relativelymoved in directions toward eachother, iluid which is beneath the piston32 will be forced out of the cylinder 3| through the passage 33 andpassage 34 in the piston I8, into the cylinder 20, for the purpose ofmaintaining constant, the pressure created in the cylinder 2U. That is,by the relative movement of the slides I4 and I5, the iluid pressure inthe cylinder 20 will not be increased, but the pressure will bemaintained constant during the operative strokes of the slides.

The cylinder 22 has communication with a fluid supply tank 35 through apre-fill valve 36.

'I'his valve may be of any desired or suitable construction, is similarto the pre-fill valve for the cylinder 20, and comprises a valve element31 having connected therewith a piston 38. The valve is adapted to beopened by suction created in the cylinder 22 when the piston 2| ismoving to lower the slide I5. However, the valve closes when suctionceases upon stoppage of piston 2| in the cylinder 22, so as to preventthe discharge of the liquid from the cylinder during the pressure strokeof the press.

A similar valve construction 39 is provided for each lof the cylinders20.

Fluid pressure is supplied to the system from any suitable source,preferably from a pump 40 suitably located, and preferably supported bythe crown of the press. All of the operating parts, including thecontrol valve mechanisms, are also located upon the crown of the press.

The pump is operated by means of a motor 4| and to one side of the pumpis connected a uid supply line 42, and the other side of the pump isconnected, by means of a pipe 43, to a relief valve 44, which may beprovided, and from this valve 44 a connection v45 leads to a four-wayvalve structure 46, the preferred construction of which valve isillustrated in Figs. 6 and 7, the valve being provided with an outletpipe 41 that leads to the tank. l

Leading from the four-way valve 46 is a pipe 48 which has communicationwith the cylinder 22 for supplying fluid pressure to the piston 2|, tooperate-the inner slide I5. Leading also from the four-Way valve 46 isanother pipe 49 which has communication with the cylinder 22 beneath thepiston head 30, and through which pipe 49 fluid pressure is supplied toraise the slidev I5.

The four-way valve 46 also has communication, by means of a pipe 50,with a three-way valve 5|, and this three-way valve 5| has communicationwith a regulating valve structure 52 by means of a pipe 53.

Leading from the regulating valve structure ,52 is a, pipe 54 which hascommunication with the cylinders 20 to supply pressure fluid to .thesecylinders above the pistons I8, and thereby create pressure upon theouter slide I4 when the latter is in engagement with the work to holdthe work. The iiuid. pressure which is thus supplied to the cylinder 20will pass through the opening 34 in the piston I8 and, by means of thepipe or passage 33, will enter the cylinder 3| below the piston 32, sothat as the outer slide is supported by the inner slide, the outer slidewill descend, by gravity, with the inner slide, thereby maintaining thetwo slides in such a relative position that the inner slide will notcontact the work in advance of the outer slide. When the outer slide I4does contact the work, Its descending movement will be arrested, Whilethe inner slide I5 will continue in its downward movement under theforce of the pressure exerted in the cylinder 22 upon the top of thepiston 2 I.

During this relative movement of the inner slide with respect to theouter slide, the pressure fluid which is in the cylinder 3| will bel'orced therefrom by the movement of the piston 32fwith respect to thecylinder, and the pressure iluid will then ilow through the passage 33and opening 34 in the piston I8, into the cylinder 20, therebymaintaining the predetermined pressure which has been created, upon theouter slide, without increasing such pressure, the action being merelythat the fluid will be transferred from the cylinder 3| into thecylinder 20.

'The slides are raised by exerting fluid pressure in the cylinder 22beneath the piston head 38 by the action of the four-way valve, in amanner tobe described. When the pressure is admitted ito the cylinder 22beneath the piston head 38, the inner slide will raise until the head oftelescoping bolt 23 contacts the top plate of the inner slide, to raisethe former. As the inner slide raises, fluid in the cylinders 20 willflow through the openings 34 and pipes 33, back into lthe cylinders 3|under the pistons 32.

As the slides descend, the pre-iill valves 36 and 39 will open, due tosuction prevailing in cylinders 22 and 20, and will close when suctionceases in these cylinders, due to momentary stoppage of slides whencontacting the work. These valves then remain closed during workingpressure stroke of inner slide I5. In order to permit the slides to beraised, it is necessary to open the pre-ll valves so that the iluidwhich is in the cylinders 25 and 22 will be discharged therefrom back-into the tank 35. This is accomplished by means of pressure uid frompipes 55 and 15.

There is provided a pilot system pump 55, which is operated by a motor55 and receives a supply of fluid through a pipe 51. A relief valve 55is provided in a pipe 55 leading from the pump 55. The pipe 59 has aconnection 55 leading to a valve I which is preferably operated by a.solenoid 52, and this valve 5I, which may be of any desiredconstruction, controls the movement of a valve element 53 in onedirection. The pipe 55 also has connection with another valve 54 whichis preferably operated by a solenoid 55 for controlling the movement ofthe valve element 52 of the four-way valve 45 in the opposite direction,the pilot pressure fluid flowing from the valve case 5i through a pipe55, and from the valve 54 through a pipe`51.

This pipe 59 also has connection with the three-way valve 5I for movinga valve element 55 in one direction, to control the ilow of fluidpressure throughy a line 59, to direct fluid pressure to operate thepre-fill valves 39 to open the latter to establish communication betweenthe cylinders 20 and the tank 35. A branch 10, leading from the pipe 50,operates the pre-fill valve 35 to open thevlatter and establishcommunicaltion between the cylinder 22 and the tank 35.

With this construction, it will be manifest that when the control'valvesare properly actuated, the pressure fluid will control the operation ofthe pre-fill valves.

The three-way valve is provided with a discharge outlet 1|, whichcommunicates with the tank 35, and the operation of the valve element 55of the three-way valve 5I is controlled, preferably, by asolenoid-operated valve 12, which may be of any desired or suitableconstruction, the valve 12ha`ving a discharge outlet 13, whichcommunicates with the tank. y

- The pipe 53 also has communication with the blank holder pressureregulating `valve 52, the latter embodying asolenoid-operated valve 15,a shut-off valve 15, a check valve 11. and an air-operated -relief valve18. The solenoid-controlled valve operates to cut off passage 8l fromcommunication with passage 19, so that when a predetermined pressure inthe cylinders 2li has been built up, the valve 15 will open by thisfluid pressure. This will establish communication between the passage 54and the pipe or passage 83, so that the fluid pressure will bemanifested upon the shut-off valve 15.

The valve 15 will then be shifted from the position shown in Fig. 3 toa. position to close Vthe passage 82, thereby cutting oi the source offluid supply to the cylinders 25 through the pipe 53. The pressure builtup in the cylinders 25, however, is controlled by the valve 15, whichitself may be set to open at any predetermined pressure.

Any number of the pressure regulating valves 52 may be provided,according to the number of blank holder cylinders, and are so arrangedthat different fluid pressures may be obtained in the differentcylinders. The difference in degree of pressures may be obtainedaccording to the predetermined opening pressures for which therespectvie relief valves 15 are set.

VA 'fter the predetermined pressures in thecylinders 25 have beenestablished, and during that part of the cycle of operation of theslides when one moves with respect to the other, in a direc- -tiontowards the work, the. fluidwill be discharged from the cylinders 2l.

'In order toprevent the fluid discharged from the cylinders 3l fromincreasing the pressure in the cylinders and, at the same time, maintainthe predetermined established pressure in these cylinders, provision ismade to permit the fluid from the cylinders 3i to flow back to the tankthrough the relief valve 18, which latter valve maintains thepredetermined pressure.

At this time the valve 15 is open, establishing communication betweenpassages 8| and 15, so that the uid thus displaced from cylinders 3lwill flow through the passage 53, thence through the valve 15 topassage, back to the tank.

' The volume of liquid in the cylinders 3i also serves as a meanstocompensate any leakage in the blank holder or outer slide hydraulicsystem.

A pressure release valve 54 may be provided for the valve 45. andpressure gauges such as those illustrated at 85 (shown more particularlyin Figs. 1 and 2), may be employed wherever necessary or desired. Ifdesired, the pilot fluid from the pipe 55 maybe directed through a pipe85 (see particularly Fig. 2), through a, filter 51,

thence to a cooler 55, before being directed back Vto the tank through apipe 55.v

The solenoids which operate the valves may themselves. be controlled inany desired or sultable manner, but preferably by means of a suitableswitch for controlling the limit of movement of the slides in directionsaway from the work. Any number of suitable switches may be provided,such as that diagrammatically illustrated at 83 (in Fig. 2), in whichthere is provided a switch arm or member 5| which may be fastened .tothe frame -of the press and is adapted to be engaged by a member 92,preferably carried by one of the slides I4-I5, to operate the switch. Asuitable switch device 53 having an operating arm 54, actuated by anadjustable cam device 55, may be provided as a release switch forcontrolling the work stripping operation. V

It is thought that the operation of this press will be clearlyunderstood from the foregoing description, but, briefly stated, it is asfollows:

When the valve element 53 of the four-way valve is in a neutralposition, that is, in the 'position shown in Fig. 5, the supply ofpressure fluid both from the main source of supply and from the pilotsupply for operating the control valves, is blocked or shut olf; thatis, the fiow of -the fluid to the operating parts is obstructed.

At this time, the supply of pressure fluid from the main pump 45 willcirculate through the pipe 45, through the valve element 53', and backthrough the pipe 41 to the tank.

To lower the slides. the valve element 53 is shifted from the neutralposition shown in Fig. 5 to the position shown in Fig. '1, which willopen the exhaust from the cylinders 22 so that the fluid will be forced,by the lowering of the piston tank.

The two slides will then descend by gravity, their weight forcingtheiluid from the cylinder 22 back to thetank, in the manner justdescribed. As the pistons I8 and 2| descend, suction will be manifestedin the cylinder- 22, which will open the pre-fill valve 35automatically, allowing the fluid to flow from the tank 35 into thecylinder to fill the space thus created in the ate the latter.

cylinder, but no pressure will be generated. At the same time, thepre-fill valves 39 in the cylinders 20 will likewise open to supplyfluid to the cylinders 20. The slides descend until the outer slide orblank holder strikes the work. At this time, the outer slide or blankholder is arrested in its movement, and the inner slide will continue tomove downwardly, operating the control switch 96, which causes areversal of the valve element 63 in the valve 46, and operates the valveelement 68 in the three-way valve 5I, through the medium ofthesolenoids. The valve 46 will' then direct the discharge from the pump 40into -the cylinders 22, through the pipe 49, to the under side of thepiston head 30, and will also direct the fluid through the pipe 5I) intothe three-way valve 5|. 'I'his will set the threeway valve tocommunicate through the blank holder pressure regulating valve 52, tothe blankholding cylinders 20, causing a pressure to be built up in theblank holder cylinders toward the work, and which pressure is greaterthan the pressure `in the pull-back cylinder 22, at the same pressureper square inch. 'I'he force of pressure in the pull-back cylinders willtherefore be less than the force of pressure in the blank holdercylinders.

The pressure in the system builds up until it reaches an amount to openthe relief valve 18 in the blank holder pressure regulating valve 52,and, obviously, this relief.valve may be adjusted to a requiredpredetermined pressure to open the same. The opening of this reliefvalve 18 permits the fluid under this pressure to flow into the shut-offvalve 16, which causes the latter to shift, thereby shutting olf thesupply of pressure fluid from the pump to the blank holder.

A check valve 11 is arranged between the relief valve 18 and theshut-olf valve 16, which traps the fluid in' the blank holder cylinders20 and prevents any return flow from the blank holder cylinders, andalso prevents any drop of pressure in the blank holderl cylinders. v

The switch 96 controls the three-way valve 5|, the four-way valve 46,also a normally open solenoid shut-olf valve 15 to close the latter,during the time of building up of pressure in the blank holdercylinders. In the line 53 between the three-way valve and the regulatingvalve 52, there is provided a pressure-operated switch 53, set at apredetermined pressure, which, however, is higher than the blank holderpressure.

With the shut-off valve 16 having closed, the pump pressure will buildup to the vpressure of the pressure-operated switch 53, and will oper-This switch in turn operates the solenoid of the shut-off valve 15, andalso shifts the four-wayvalve -46 to cause the inner slide I5 to movedownwardly, in a manner already described. The outer slide I4 will nowbe locked, with full predetermined pressure against the Work.

The four-way valve 46, being now positioned as shown in Fig. '1, willexhaust the fluid from the pull-back cylinders'2Il and direct the volumeof the pump discharge into the main cylinder 22 of the inner slide I5,thereby moving the inner slide downward by pressure and against theresistance of the pressure-maintaining cylinders 3|, thereby eliminatingthe possibility of any dropping of the inner slide by gravity. The innerslide I5 will then be forced downwardly by fluid pressure from'the pump,through the pipe 48, causing a displacement in the pressure-maintainingcylinders 3 I, which displacement is discharged in the blank holderpressure-regulating valve 52.

back into the tank, in the manner heretofore described.

This maintains the predetermined pressure in the blank holder cylindersduring another draw stroke of the inner, or punch, slide. The drawstroke is terminated when a predetermined pressure is reached on theinner slide I5, at which time a suitable switch 9|I9| will cause thevalve element 63 in the four-way valve 46 to be shifted into a positionto obtain the up-stroke of the inner slide.4 The main cylinder 22 of theslide I5 is thereby connected with the tank, releasing the pressure fromthe main cylinder.

At the same time, the pump discharge is connected with the cylinder 22,to direct fluid pressure under the piston head 30, to pull back theslides, through the pipe 49, which automatically, through the pipe 10,also connects the pump with the pilot piston for operating' the pre-fillvalves 36 to open the latter, allowing the fluid in the main cylinder 22to escape into the tank, while the inner slide I5 is being thus pulledback or raised by the pressure in the cylinder 22 under the piston head30.

The pump discharge also passes from the four'- way valve 46 through thethree-way valve 5I and the blank holder pressure-regulating valve 14(lifting the check valve 11 in the latter), into the blank holdercylinders 20, thereby maintaining the pressure in the blankholder-cylinders and, consequently, on the outer slide I4, holding itdown, thus maintaining pressure on the work, while the inner slide I5 isbeing extracted or moved away from the work.

During this lower portion of the up-stroke of the irmer slide I5, theblank holder or outer slide I4 remains down; consequently, the rams ofthe pressure-maintaining lcylinders 32 are being withdrawn from theircylinders 3| and the voids created therein are being lled with pressurefluid from the pump, through the blank holder cylinders and their hollowblank-holding rams 29. This supply of pressure fluid into thepressure-maintaining cylinders 20 results in an uplifting force for theinner slide I5, by acting upon the pistons 32 in thepressure-maintaining cylinders 3|, which results, during this part ofthe stroke-only, in a. lifting force in excess of the lifting force ofthe pull-back cylinders 20, which is desirable in stripping the workfrom the punch or die carried from the inner slide I5. During thisoperation, the outer slide is being held down against the work by fluidpressure from the pump 48.

After this stripping stroke has been finished by the inner slide, aswitch `93---94 will be operated to cause the three-way valve element 68to be shifted from the position shown in Fig. 4 to the position shown inFig. 3, when the pump discharge will be diverted to the pilot pistons ofthe pre-fill valves 39, through the line or pipe 69, for operating thepre-fill valves 39 of the blank holder cylinders 30. These valves,however, will not open until the pressure-maintaining cylinders 3| havebeen relieved by the further upward movement of the inner slide I5 whichpulls the pistons 32 out of the pressure-maintaining cylinders.

Pipes 39*L lead from the pre-fill valve casings 39 and discharge backinto the tank, and an gerflow 91 maintains a liquid level in the tankWith the present construction, and due to the fact that pressure iscreated in the cylinders 2l by the pump, and as this pressure ismaintained by the iluid from the pressure-maintaining cylinders'll, thecylinders 2li are small in area; consequently, the additional forcerequired by the `inner slide" I5, to displace the smaller amountparativelyjsmall pump and motor, resulting in a press much moreeconomical in power consumption than other presses. Furthermore, astheouter slide pressure is independent oi the inner slide pressure, eachpressure can be adjusted independently ot the other.

With this improved press, the outer or work clamping slide ismechanically suspended from the inner or punch carrying slide by meansof the rod or bolt, any number of which may be provided, and arerelatively movable.

In one stroke of the press, both the outer and inner slides descendsimu' taneously until the outer slide contacts the Work.

1n that instant, the movement of the outer or clamping slide isarrested. In the same instant, the pressure supply pump will dischargeinto the cylinders which create the pressure upon the outer or workholding slide, generating the clamping pressure up to a predeterminedfixed amount of pressure, in a short period of time. At the instant whenthis predetermined clamping or holding pressure is reached, the innerslide again starts its own downward stroke, because the pump dischargewill have been disconnected from/"the:

pressure creating cylinders for the clamping or work holding slide, andalso will have been automatically connected with the hydraulic cylindervwhich actuates the inner slide.

During this further downward stroke of the .inner slide, this slideactuates an auxiliary hydraulic piston and cylinder element of smallerdiameter, any number of which may be provided. The uid discharged fromthe auxiliary cylinder is delivered' into the cylinders of the clampingor work holding slide for maintaining the established clamping pressure,but does not generate pressure to operate the clamping slide. The excessfluid ejected from the cylinders, the pistons of which are actuated bythe relative movement of developed to its predetermined value from thepressure supply pump, whereupon the source of.

pressure is disconnected from the clamping or work holding slidefand isconnected to the inner or punch slide operating cylinders. As a result,the inner or punch slide descends and causes the `pressure-maintainingiluid to pass from its auxiliary cylinder into the main clampingcylinder, without increasing the pressure in the clamping cylinder.

There has been described only one of the regulating valve structures 5land its connection with one of the pressure creating cylinders 20 oftheouter slide, and two only of such valves are shown in Fig. 2 of thedrawings. Itis to be understood, however, that as many of these valves5l may be used as desired; that is, one for each of the cylinders 20. Inthe present type ot press, there are provided four cylinder and pistonunits I 3-2I. one for each corner of the outer or work holding slide.This renders it possible to establish different predetermined pressuresin the respective cylinder and piston umts |8-2II, as may be desired, aseach valve controls the fluid pressure from the common source to therespective cylinder and piston units l820. By adjusting or settingtherespective valves 18, according to the degree of pressure it is desiredto establish. such pressure maybe varied in the dierent cylinder andpiston units. f

Thus it willl be seen that, with this arrangement, pressure will bebuilt up to the pressure at which the work holding or outer slide switch53 is set to operate. at which time this switch will trip or operate,causing the four-way valve 46 to shift, to allow the slide to continuein its downward movement.

While the preferred form of the invention has been herein shown anddescribed, and the preferred hydraulic systems and arrangements of pipesand valves have also been shown and described, it is to be understoodthat various changes may be made in the details of construction and inthe combination and arrangement vof the several parts, within the scopeoi.' the claims, without departing from the spirit of this invention.

What is claimed as new is:

1..In combination in a press, a slide. a work clamping slide supportedthereby for movement therewith and wit'lri'espect thereto,- means formoving the ilrst said slide to move the clamping slide into a clampingposition, cylinder and piston umts connected with the clamping slide,means for creating and means for maintaining in the said units apredetermined fluid pressure upon the clamping slide. an auxiliarycylinder and piston unit operable by the relative movement of theslides, means operating when said predetermined pressure is established,to disconnect the source of fluid pressure supply from the Ilrst saidunits, and for connecting said source of supply to a cylinder and pistonunit for actuating the ilrst said slide to further move the hitter in adirection toward the work, and means whereby upon relative movement ofsaid slides after said predetermined iluid pressure has beenestablishedA upon the work clamping slide, to transfer the pressureiluid from said auxiliary cylinder to the cylinder which fluid pressureupon the work clamping slide has been created, to compensate leakage inthe clamping slide cylinders while maintaining the said predeterminedpressure in the last said cylinders against variation.

2. In combination in a press, a slide, a work clamping slide supportedthereby for movement therewith and with respect thereto. means formoving the rst said slide to move the clamping* slide into a clampingposition, cylinders and pistons connected with the clamping slide, meansfor creating and means for maintaining in the said cylinders apredetermined fluid pressure upvon the clamping slide, an auxiliarycylinder and piston unit operable by the relative movement Aoi' theslides, means operating when said predetermined pressure is establishedin the clamping slide cylinders, to disconnect the source of iluidpressure supply from the rst said cylinder, and

Afor connecting said source of supplyto a cylinder and piston unit foractuating the ilrst said slide to further move the latter in a directiontoward the work, means whereby fupon' relative movement ofsaid slidesafter said predetermined fluid pressure has been established upon thework clamping slide, -to transfer the fluid from said auxiliary cylinderto the cylinder in which fluid pressure upon the work clamping slide hasbeen created, to compensate leakage in'the clamping slide cylinderswhile maintaining unvaried the said predetermined fluid pressure in theclamping slide fluid pressure cylinders, means embodying valve mechanismfor supplying :duid to the cylinders to fill the space created by therelative movement of the cylinder and piston element, and means foropening said valve.

3. In combination in a press, a slide, a work clamping slide supportedthereby for movement therewith and with respect thereto, means formoving the first said slide to move the clamping slide into a clampingposition, cylinder and piston means connected with the clamping slide,means for creating and means for-maintaining in the said cylinder apredetermined fluid pressure upon the clamping slide, an auxiliarycylinder and piston unit operable by the relative movement of theslides, means operating when said predetermined pressure is establishedin the clamping slide cylinders, to disconnect the source offluidpressure supplied from the clamping slide cylinders, and forconnecting said source of supply to a cylinder and piston unit foractuating the ilrst said slide to further move the latter in a directiontoward the work, means whereby upon relative movement of said slidesafter said predetermined fluid pressure has been established upon thework clamping slide, to transfer the pressure uid from said auxiliarycylinder to the cylinder in which fluid pressure upon the work clampingslide has been created, whereby to compensate leakage in the clampingslide cylinders, while the said predetermined iluid pressure will bemaintained in the clamping slide fluid pressure cylinders, meansembodying valve mechanism for supplying fluid to the cylinders to fillthespace created by the relative movement of the cylinder and pistonelement, and means embodying a fluid pressure system for opening saidvalve.

4. In combination in a press, two movable slides, a source of. supply ofuid pressure common to the slides, means individual to the slides forcausing the fluid pressure from said source to be directed to therespective slides to operate thereupon, means whereby a predeterminedfluid pressure may be established upon the respective slides, and apiston and cylinder unit one of the elements of which is connected toand movable with each of the slides, said units being relatively movablein response to the relative movement of the slides, said unit operatingto transfer fluid from a supply to the fluid pressure operating means ofone of the slides for compensating leakage of the fluid pressure in thelast said means and for maintaining against augmentation the saidpredetermined pressure upon the last said slide for a predeterminedperiod in the retraction movement of the other of the slides.

5. In combination in a press, two movable slides, a source of supply offluid pressure common to the slides, means individual to the slides forcausing the fluid pressure from said source to be directed to therespective slides to operate thereupon, the fluid pressure actuatedmeans of one of said slides embodying a plurality of cylinder and pistonunits, means whereby a predetermined fluid pressure may be establishedin said units, the last said means embodying mechanism adapted to be setto obtain different predetermined iluid pressures in said units, andsupplemental cylinder and piston units to which the fluid pressure fromsaid source is also directed. said supplemental units being actuated bythe relative movement of the slides and operating to transfer fluid fromsaid supplemental units to the first said units, to compensate leakagein the latter and for maintaining said predetermined fluid pressure insaid units against augmentation during a predetermined retractionmovement of one of the slides.

6. In combination in a press, two movable slides, a source of supply offluid pressure common to the slides, means individual to the slides forcausing the fluid pressure from said source to be directed to therespective slides t o operate thereupon, the fluid pressure actuatedmeans of one of said slides embodying a plurality or' cylinder andpiston units, means whereby a predetermined fluid pressure may beestablished in said units, the last said means embodying valve mechanismadapted to be set to obtain different predetermined fluid pressures inthe respective cylinders of said units, supplemental cylinder and pistonunits in which said predetermined pressure is also established, saidsupplemental cylinder and piston units being operable by the relativemovement of the slides for transferring fluid from said supplementalunits to the flrst said units, to compensate leakage in the first saidunits and to maintain said predetermined fluid pressure therein, whilethe said predetermined fluid pressure is maintained againstaugmentation, and means for causing iluid pressure from the first saidsource of supply to pull back one of said slides.

'7. In combination with a press having two independently movable fluidpressure operated sure to be exerted upon one of the rams, a cylinderand piston unit, one element of which is connected to and movable witheach of the rams,

said cylinder having communication with one of said rams and being alsosupplied with fluid from said source, and in which cylinder saidpredetermined fluid pressure is also established, the Auid from 'saidcylinder being transferred therefrom by the relative movement of theelements of said unit, caused by the relative movement of the rams, tocompensate leakage in one of said rams, while the said degree of saidpredetermined pressure upon the last said ram is maintained againstincrease during a predetermined portion of the retraction movement ofthe other of said rams.

8. In combination with a press having two independently movable fluidpressure operated rams, a source of supply of fluid pressure common tothe rams for applying pressure thereupon, means embodying valvemechanism adapted to be set to establish a predetermined pressure to beexerted upon one of the rams, a cylinder and piston unit, one element ofwhich is connected to and movable with each of the rams, said cylinderhaving communication with one of said rams and being also supplied withfluid from said source, and in which cylinder said predetermined fluidpressure is also established, the fluid from said cylinder beingtransferred therefrom by the relative movement of the elements of thesaid units, caused by the relative movement of the rams, to compensateleakage in one of said rams, while the said degree of said predeterminedpressure upon the last said ram is maintained against increase during apredeter- Y.

mined portion'oi the retraction movement of the other or the rams.

9. In combination with a press having two slides independently movable,a ram for moving one of the slides, a-plurality of ram units for movingthe other slide, a source of supply of iluid pressure common to the ramsand ram units for creatingv pressure thereupon, means individual to thesaid ram units and adapted to be set whereby dierent predetermined fluidpressures may be established in the respective said units, a cylinderand piston unit' individual to each of the rams of the flrst said unitsand in which cylinders said predetermined uid pressure is alsoestablished,

one of the elements of the last said unit being connected to each of theslides, the fluid pressure from said cylinders being transferred to therespective rams of said ram units upon relative predetermined iluidpressure in said cylinders p and in the respective rams of said ramunits being maintained against increase by such transfer of the fluidduring a predetermined period in the retraction movement of the rams.

ALOIS K. NOWAK. THOMAS W. BANNON.

